1. Technical Field
The present invention relates generally to communication networks, and more particularly to the dynamic resource allocation in a network based on a centralised transmission resource allocation.
2. Related Art
Wireless Local Area Networks (WLANs) have recently experienced a rapid development mainly due to the increase of the bandwidth they can offer. Concurrently, the number of users and the diversity of applications have grown. As a consequence, a WLAN simultaneously transports a large number of data flows generated by several types of applications. It results there from that the transmission resource which remains relatively scarce, requires a very efficient allocation mechanism. On the other hand, such a type of network as a wireless network provides a transmission resource not very reliable due to the radio medium. It results from it that some transmission errors can occur on one or several data flows.
Herein below, the term “data flow” will refer to a data transmission originating from a given user for a given application between a transmitter and a receiver and the term “flow type” will refer to a data transmission originating from a given type of application, independently of the corresponding users.
All applications transport over such a network can be very different regarding the Quality of Service (QoS) requirements. Actually, whereas a simple best effort service can be sufficient for data applications transported by TCP for example, multimedia applications such as interactive video and sound transmission can require a more stringent service and a better QoS. The transmission corresponding to the applications requiring a good QoS are based on such key parameters as the maximum throughput and the maximum transmission delay. Consequently, for such applications a network is classically in charge of guaranteeing these key parameters.
On the other hand, a radio channel propagation can be very fluctuating. Consequently, the physical or PHY layers developed for recent WLANs are able to dynamically support different coding methods in order to efficiently adapt to radio channel propagation and to fit in different environments. It results there from that the Medium Access Control or MAC layer can use an available PHY resource which is variable along time and which will be referred to as transmission resource herein below. In a centralised allocation scheme handled by a Radio Resource Management or RRM unit, the available transmission resource can be shared by the RRM unit between the different user data flows generated by applications. Moreover, the RRM unit can take into account the requirements of the different applications in order to optimise the shared resource transmission. Classically, such a RRM unit implements a scheduling mechanism, which defines one or more principles to share a transmission resource.
Various scheduling mechanisms have already been proposed to share the transmission resource in a WLAN network. More particularly, the document “An overview of scheduling algorithms in Wireless Multimedia Networks”, IEEE Wireless Communications, October 2002, written by H. Fattah and C. Leung, presents a scheduling mechanism based on some compensation schemes. A compensation scheme classically refers to a scheme able to compensate transmission delay experienced by a given data flow, due to transmission errors for example, among a list of data flow. More particularly, in the document cited above, an objective of the compensation schemes is to achieve fairness between data flows generated by applications regarding the errors due to radio channel degradations. Stated otherwise, a scheduling mechanism ensures that transmission resource is preferably allocated to a data flow experiencing transmission errors in order to compensate these errors.
In the document S. Lu, T. Nandagopal and V. Bharghavan, “A wireless fair service algorithm for packet cellular networks,” in Proc. of ACM MOBICOM '98, October 1998, in the document P. Ramanathan and P. Agrawal, “Adapting packet fair queuing to wireless networks,” in Proc. of ACM MOBICOM '98, October 1998, in the document T. S. Eugene Ng, I. Stoica, H. Zhang, “Packet fair queuing algorithms for wireless networks with location-dependent errors,” in Proc. of IEEE INFOCOM '98, March 199, and in the document T. Nanddagopal, S. Lu, V. Bharghavan, “A Unified Architecture for the Design and Evaluation of Wireless Fair Queuing Algorithms,” in Wireless Networks, vol. 8, pp. 231-247, 2002, scheduling mechanisms are proposed which rely on a swapping mechanism. In these documents, a scheduling mechanism is proposed to handle data flows experiencing channel errors to data flow with a clear channel. Then, different methods are presented to restore equity between data flows and to give back more transmission resource to penalised data flows once their channel is clear.
In these proposals, the same scheduling mechanism is applied to all data flows. However, as it is already written above, different applications and different users in a given network do not require same QoS constraints. On the other hand, the effects induced on applications by a scheduling mechanism are not the same ones according to the type of applications. Considering one of major issues is to fulfil the application requirements, it could be profitable to define different classes of applications and different fairness principles in order to apply to each of these classes a corresponding fairness principle. Such a scheduling mechanism has been already described in D. A. Eckhardt and P. Steenkiste, “Effort-limited fair scheduling (ELF) for wireless networks,” in Proc. of IEEE INFOCOM 2000, March 2000.
Regarding the previous description, a lot of propositions for wireless scheduling mechanisms have been already discussed and proposed. However, these types of mechanisms can always be improved depending on different constraints and objectives to be solved.